1. Field of the Invention
The present invention relates to rotary drum filters of the center valve type, and more particularly to a replaceable valve seat for the valve member of such a filter.
2. Description of the Prior Art
Rotary drum filters of the center valve type are commonly used in the pulp and paper making industry to separate wood pulp from its filtrate. The drum filter comprises a rotary drum partially submerged in a tank of pulp slurry. The drum has axially extending filtrate compartments spaced about its periphery, with such compartments covered by a filter screen. Each filtrate compartment opens into a center circumferential channel of the drum in communication with a source of subatmospheric pressure. An arcuate stationary valve member is mounted within and extends partially about the channel. As the drum rotates about its axis with subatmospheric pressure applied, the screen rotates through the pulp slurry, collecting a wet mat of fibers from the slurry. As the screen emerges from the tank, filtrate is drawn through the screen and compartments into the center channel and from there discharged through suitable piping from the drum to remove liquid from the mat. As the drum continues its rotation, the stationary valve member periodically blocks off the filtrate compartment outlets from the source of subatmospheric pressure, thereby enabling removal of the pulp mat from the surface screen.
In conventional center valve filter drum construction, as shown, for example, in FIG. 3 of the application drawings, and also as shown in slightly different form in Turner, Jr., U.S. Pat. No. 3,327,863, the valve seat portions of the drum within the central channel, which embody the wear surfaces in sliding contact with the stationary valve member, are fabricated as integral portions of structural members of the drum. However, such valve seat surfaces are commonly subject to rapid wear because of their continual exposure to highly abrasive and often chemically active filtrate liquids. Oftentimes the operating life of such valve seats is exceedingly short as compared to the overall useful life of the filter drum itself. However, because such valve seats are usually integrated with the structural members of the drum, when they wear out the drum must be taken out of service, and either replaced with a new drum or shipped to a repair facility for rebuilding of the channel portion of the drum. Whether a drum is replaced or only rebuilt when its valve seat portion wears out, either choice is expensive and entails considerable lost production time.
Accordingly, a primary object of the present invention is to provide a rotary drum filter of the center valve type with easily replaceable valve seats, which can be replaced quickly and easily in a minimum amount of time, and without removing the drum filter from its production line.
A prior art U.S. Pat. No. 3,327,862 does suggest providing a rotary drum filter of the center valve type with a detachably mounted pair of inner trackway portions upon which a stationary center valve member rides. However, the detachable portions of the ways shown in such patent comprise only a portion of the valve seat. Other portions of the valve seat structure are integrated with the structural members of the drum, and therefore have the same drawbacks as other prior center valve drum filters previously mentioned. Thus, in drums as shown in the aforementioned patent, valve seat portions which become worn out would still require a considerable amount of rebuilding of the channel portions of the drum filter. It is therefore apparent that the only purpose of the detachable inner trackway portions in the aforementioned patent shown is to facilitate installation and removal of the stationary center valve member because of the peculiar internal mounting of such valve member within the drum.
Accordingly, there is a need for a center valve rotary drum filter having an entirely replaceable valve seat so as to prolong the useful life of such filters.